What Causes Green Slimy Vaginal Discharge During Pregnancy?

I am 33weeks pregnant, second pregnancy. First child was born at 29 weeks. I take weekly injections and have been put in a pill I take every 6 hours to stop my contractions. I 1cm dilated and 50% effaced. I lost my mucus plug 2-3 weeks ago. Today when I went to the bathroom I noticed a light green slimy discharge which I haven't seen before. What could it be? When I walk I feel a lot of pressure on my lower stomach.